Purification of polymers



Nov. 15, 1960 P. F. WARNER ETAL 2,960,454

PURIFICATION ,QF PoLYMERs Filed March 28, 1957 EVS nited States Patent Oce PURIFICATION F POLYMERS Paul F. Warner, Phillips, and John T. Middlebrook, Borger, Tex., assignors to Phillips Petroleum Company, a corporation of Delaware Filed Mar. 28, 1957, Ser. No. 649,204

Claims. (Cl. 204-186) This invention relates to the removal of impurities from polymers. In one of its more specific aspects, this invention relates to the removal of .gels from solutions of hydrocarbon polymers. In a still more speciic aspect, this invention relates to the simultaneous removal of gels and inorganic materials from solutions of olen polymers.

This application is related to 'an application of P. F. Warner, Serial No. 643,144, tiled February28, 1957, now abandoned; I

The polymerization of butadiene to form liquid polymers of butadiene is well known and a preferred process is disclosed and claimed in U.S. Patent 2,631,175, issued March 10, 1953, to W. W. Crouch. The process as described comprises polymerization of 1,3-butadiene in the presence of an alkali metal catalystuand a suitable polymer solvent or `diluent, the reaction being Acarried out under carefully controlled reaction conditions, particularly temperature, catalyst conditions and concentration, quantity of solvent, and rate of butadiene addition; recovery of the product by some appropriate means such as by treatment with a quantity of water followed by -ntroduction `of carbon dioxide to react with the alkali metal and organo-alkali metal compounds and to precipitate alkali metal carbonates, removal of the precipitate, and stripping to separate the diluent from the liquid polymer. When operating according to the process of the above described invention, a liquid polymer of high molecular weight is produced. The polybutadiene ythus produced is a substantially colorless transparent liquid.

One of the problems encountered in the production of high molecular weight liquid olen polymers is that of removing the catalyst used in the polymerization. Gel is `sometimes produced in the polymerization and it is desirable to remove this gel at least for certain uses. If the catalyst is removed by gravitational means, i.e., centrifuging, settling, etc. at -least a substantial part of the gel remains in suspension. Filtering normally removes both gel and catalyst but if a substantial amount of gel is present, the lter medium plugs almost immediately upon the introduction of the solution, and therefore, the filtering medium cannot be used under these circumstances with any degree of success. Furthermore, filteringV is not a satisfactory means of catalyst removal in some polymerization processes such as in the polymerization of butadiene to a high molecular weight liquid polybutadiene in the presence of nely divided alkali metal catalyst. v

Itis therefore an object of this invention to provide an improved method for Ithe removal of. 4gel from solutions of polymers. It is also an object of this invention to provide an improved methodior the removal of catal-yS- frgm the polymer produced m a polymenzatlon rethe inorganic catalyst residue material, or -a combination actioh. A further object of this invention is the provision of a method for the simultaneous removal of gel and catalyst from a solution of a polymer. Other and further advantages and objects of. this invention will be apparent'to one skilled in the art upon study o f the dis-i closure'of the present invention.

Broadly, the invention contemplates the removal of gel from a solution containing the same in admixture with a polymer by subjecting the solution to which a multi-v valent cation has been added to an electrostatic field whereby the gel is precipitated or agglomera-ted and is simultaneously or subsequently removed.

Without the use of the multivalent cation, the process is the same as described in the application 'above-mentioned of P. F. Warner. It has been found in operating the Warner invention that some solutions are difcult to treat using that invention. For instance, some reactor eluents contain -so much gel that the simple electrical precipitator treatment is insufficient.

We have discovered that an improvement is obtained by treatment of the reactor eluent, following quenching, with a multivalent cation. We have found improvement wi-th all of the multivalent cations we |have tried and the invention is applicable to all of these cations. Salts which can be usedinclude aluminum acetate, aluminum benzoate, aluminum bromide, aluminum ferrocyanide, aluminum nitrate, aluminum oxalate, aluminum sulfate, barium acetate, bariumV carbonate, barium chlorate, barium chloride, barium formate, beryllium chloride, beryllium oxalate, beryllium sulfate, bismuth acetate, bismuth sulfate, bismuth chloride, cadmium benzoate, cadmium chloroacetate, cadmium formate, cadmium sulfate, cadmium sulte, calcium carbonate, calcium chlorate, calcium chloride, calcium malonate, calcium nitrite, calcium sulfate, chromium acetate, chromium chloride, chromium nitrate, chromium sulfate, cobalt bromide, cobalt chloride, cobalt sulfate, ferrous acetate, ferric chloride, ferrie oxalate, lead acetate, lead'nitrate, magnesiurn acetate, magnesuim benzoate, magnesium chloride, magnesium perman'ganate, magnesium suliite, manganese iodide, manganese sulfate, mercurio bromide, mercurio chloride, nickel chlorate, nickel chloride, nickel sulfate, tin bromide, tin chloride, tin sulfate, tin tartrate, titanium tetrachloride, zinc acetate, zinc borate, zinc carbo-nate, zinc chloride, zinc sulfate, and the like. Complex salts,y of these metals, such as alum, can also be used.

The drawing is a schematic flow vdiagr-am of la preferred embodiment of the invention.

The present invention is particularly applicable to -the simultaneous removal of gel and catalyst residue froml solutions of high molecular weight polybutadiene in a polymerization process effluent. It is also applicable to the removal of gel from a catalyst-free and solvent-free product. If a solvent-free product is used, it must be of such a molecular weight that t-he viscosity is sufficiently low to permit migration of the impurity therethrough 4so yas to accomplish agglomeration of the gel particles; In processing high molecular weight liquid polybu-tadiene (molecular weight-1,000 to 3,000), it is preferred vto have the solution contain not more than about 40 to 50 percent polymer. The process is equally applicable to the removal of gel from a quenched reactor effluent during the manufacturing process or from the iinished product. In those cases where the gel removal step is used in conjunction with the manufacturing process, it vis preferred to install it immediately after the reactor effluent is quenched, because the catalyst residue material is also simultaneously removed and the use ofv conventional catalyst residue removal equipment is thereby' eliminated. The electrostatic eld can be used either-for agglomeration of the gel particles or for precipitation' lof of the two. Operating conditions can be adjustedV so that all of the impurities are deposited on the electrodes or operating conditions can be adjusted so that at least a major portion of the material leaves the electrostatic `field in an agglomerated condition so thatit caneasily Patented Nov.` 15, 1960*` 'be removed by conventional means such as a centrifuge or a coarse iilter medium.

The reactor eiiiuent stream is treated so as to quench the reaction by destroying the active catalyst as quickly as possible. Thus, the reactor eluent stream is treated with a suitable material, such as methyl alcohol, so as to convert the alkali metal catalyst to an alkali metal salt, such as sodium methylate (sodium methoxide). Other suitable materials for quenching the reaction by destroying the catalyst include oxygen-containing materials such as low molecular weight alcohols, formic acid, acetic acid, carbon dioxide, and methyl carbitol.

Following the quench step, the metal salt is added, frequently as an aqueous solution. Thek salt can be added alone or salt solution can be used to wash the effluent from the quench step. Generally, 20 to 500 milliliters of salt solution are added per gallon off reactor eiiluent, said salt solution containing to 50 grams of the metal salt per gallon. In some cases, it is desired to heat the eiliuent from the quench step and this can easily be done by heating the material to the reflux temperature. This last step is not essential, however, in the practice of our invention.

It is believed that the impurities referred to as gels result from cross-linking of the polymer produced in the reaction and the reason for quenching the reaction immediately following the reaction vessel `is to discourage formation of these materials. An indication of the amount of gel present in a polymer, and consequently, the filterability of the polymer, can be obtained b y making a thin lm of the polymer and determining the frequency of detectible .particles referred to as fish eyes. The iish eye count does not always reilect the true lterability of the product but does provide an indication of the presence of gels which can aiect iilterability. In every instance, however, polymer treated according to the present invention has displayed improved tllterability characteristics and lower iish eye count as compared to the charge material. Although we do not fully understand the forces which bring about the agglomeration and precipitation of the gel Vfrom a polymer solution, we have found that subjecting the polymer solution to which a multivalent cation has been added to an electrostatic field results in a preferential accumulation and separation of cross-linked polymeric material referred to as gel from linear polymers. Furthermore, we have found that a direct-current electrostatic eld accomplishes the desired agglomeration whereas an alternating-current does not accomplish the desired selective accumulation. Voltages in the range of 800 to 33,000, based on one inch electrode spacing, can be used for gel and catalyst removal. v

The attached drawing illustrates one embodiment of the invention, however, it will be obvious to those skilled in the art and in possession of the disclosure that numerous other embodiments are within the scope of the invention. The process described in connection with the drawing relates to the polymerization of butadiene to a viscous liquid in the presence of a finely divided metallic sodium catalyst and la normal heptane diluent, but the description of the embodiment should not be considered as limiting the invention. It will be understood that various valves, pumps, and other equipment` inherently necessary inthe operation of the process will not be illustrated because it is within the skill of one acquainted with this art to provide such necessary auxiliary equipment.

A butadiene polymerization reactionsuch as that described in U.S. 2,631,175 is conducted in reactor 1 and the eiliuent from the reactor is passed through a conduit 2 to separator 3 together with a stoichiometric .excess of quench material, such as alcohol, added to the reactor effluent via conduit 4 so as to convert all `of the sodium catalyst to sodium methylate. Normally, only non-condensible gases such as hydrogen are vented from the separator 3 via conduit 5; however, if desired, any excess of alcohol and even a portion of the normal lhep-tane dilueut can also be removed via conduit 5. The resulting polymer solution is passed via conduit 6 to contactor 19 to which the treating agent is supplied via conduit 20. Excess treating agent, if used, can be removed through conduit 35, if desired. The efiiuen-t from contactor 19 is passed via conduit 6' to a two-stage electrical precipitator comprising stages 7 and 8. The precipitators comprise center electrodes 9 and 9', annular electrodes 10 and 10', insulators 11 and 11', and power supply means 12 and 12'. In the embodiment shown, two sections are illustnated, but any number, including one, can be used if desired. ln the embodiment shown, the first section or stage is operated principally as an emulsion breakingv apparatus wherein a Voltage gradient in the range 1100 to 8800 volts is used. The term voltage gradient is used to denote the voltage used where the electrode spacing is one 1nch. Thus a voltage of 1000 volts for 0.5 inch spacing would be equivalent to a voltage of 2000 volts Ifor l inch spacing. The permissible voltage in the first stages of precipitation is normally limited due to the conductivity of the solution. After a substantial portion of the electrically conductive materials have been removed, a voltage gradient in the range 11,000 to 28,000 can be used satisfactorily. Direct current is used and both gel andr catalyst deposit on the negative electrode or at least migrate toward the negative electrodes. When the electrodes have deposited thereon a substantial amount of gel and catalyst, the current is shut off and the precipitators are then ushed with a suitable material. This material is preferably the same as the polymer solvent but other liush materials can 4he used when desired. It is also within the scope of the invention to reverse the ow of current during the washing step but -it is preferred to shut off vthe current entirely. The ush material leaving the precipitators can either be discarded or passed to a suitable recovery zone 13.

'I'he optimum time for shutting otl the current and ushing the precipitators -with Wash material can be determined by various means. Thus, a sample stream 21 can be diverted from product line 15 and continually passed through a iilter medium 22. When the edectiveness of the precipitators begins to decrease as a result of material deposited on the electrodes, the increased back pressure created in the filter medium can be converted to a signal by pressure transducer 23 to operate automatic cycler 24 so as to shut off the current to the precipitators to close valve 25 stopping the feed of polymer to the precipitators and to open valve 2,6 so as to start a iiow of flush material to wash the electrodes of the precipitators; after which the ow of the wash material is discontinued, potential is again applied to the precipitators and the ow of polymer solution is resumed. Another method of determining the saturation point of the precipitators is to direct a `beam of radiation through the precipitators to a detector, such as an electric eye, so Vthat an interruption in the beam of radiation caused by accumulation of gel and catalyst will initiate operation of the automatic cycler. Thus, radiation can be caused to pass from source 31 through sight glasses 32 and 33` to detector 34.

The polymer solution leaving the precipitators via conduit 15 is now essentially gel free and catalyst free and is passed to a water wash vessel 14. The water washed solution is then passed via line 1,6 to separation zone 17, wherein the product is recovered essentially solvent-free and the solvent is recovered and all or a portion of it is recycled to reactor 1 via conduit 18.

The following specic examples further illustrate the advantages of the process of this invention.

EXAMPLE I A series of runs were made to demonstrate the improvement obtained by the practice yof our invention. The apparatus was substantially that as shown in the single figure using electrodes 10` and 10' of stainless steel tubing having 'an outside diameter of `one inch and f/sinch copper tubing for electrodes 9 and 9. `Direct current voltages were applied between the electrodes of 800 and 5000 volts, the voltage being applied in each case being shown in the accompanying table. yIii each run, the electrode spacing was 0.34 inch. The data for these runs 6' a linear polymer of butadiene it is also applicable to the separation of cross-linked polymer from other linear polymers, such as a solution of solid polyethylene produced in the presence of a chromium oxide catalyst. A process are showninTable I. 5 for producing solid, linear polymers of ethylene is de- Table I First Stage Second Stage Charge Fish Effluent Amount, Percent Run Pretreatment eyes Ash Salt grams Fish Der DS1 eyes sq. in. Volts Microamp. Volts Microamp. Fish As gallon Removed eyes Wt.

per Percent sq. in.

1 Plant on gas separator 100 4. 0+ 800 50o-4,000 5,000 250 10 0.03 `00.0

efuent (Reactor efuentnkilled with meth- 5110 2 Reactor efiuent quenched 400 2. 0+ 800 100-200 5,000 250 92 0.067 77.0

with excess methanol n ind rei-lured several 3 ofi gas separator einueiit 100 4.0+ 5,000 250 5,000 250 i 0.007 A101,.6H0 20 99.0

treated with 100 ml.

methanol, 100 inl. water and salt. 4...-.. Reaetorefuent quenched 400 2. 0+ 800 4 5,000 250 1% 0.077 AlGhHgO." 20 99. 75

with methanol 50 ml./

gal. Retluxed with 100 ml. methanol-i-salt.

Examination of this table demonstrates the improvescribed in copending application Serial Number 573,877, ment obtainable by the practice of our invention. Runs tiled March 26, 1956.

1 and 3 were carried out on the same feed material, alu- The invention is also applicable to the removal of gel minum chloride in aqueous solution being added to run 3 5 from synthetic rubber, such as butadiene/ styrene coand runs 2 and 4 are i'uii on the same 4feed material with 3 polymers. In the removal of gel from rubber the preaqueous aluminum chloride solution being added in run 4. ferred method is to dissolve the dried crumb rubber in a Practically complete removal of fish eyes was obtained suitable solvent, such as benzene or toluene and to pass the in runs 3 and 4 whereas, when no salt was used, only 77 solution through the precipitators so as to separate and repercent and 90 percent removal was obtained. In these move the gel. The precipitator effluent is then flash disruns, the reactor eluent was about 50 weight percent 40 tilled to remove the solvent and recover the gel-free liquid polybutadiene in normal heptane. The liquid polyrubber.

butadiene was prepared by sodium catalyzed polymeriza- As many possible embodiments can be made from this tion according to the method of Crouch, 2,631,175. The invention without departing from the scope thereof, it is solution after treatment with the salt was fed to the preto be understood that all matter herein set forth -is to be cipitator at approximately 200 milliliters per hour. interpreted as illustrative and not as unduly limiting the EXAMPLE II invention. We claim:

Using another run, the material following the quench l. In the process for producing polybutadiene wherein step was washed with water saturated with aluminum 1,3-butadiene is polymerized in a polymerization zone in chloride. A product having 1.2 sh eyes per square inch an linert solvent for the polybutadiene land wherein gels was obtalned. insoluble in said solvent are produced as a byproduct of EXAMPLE III said polymerization, the improvement which comprises Using the material of Example II, a wa-sh step was used Wlihdrawmg from said poiymenzation Zon? 'f1 mixture O f wherein a saturated solution of aluminum sulfate was smd Solvem and gel-addlng, a salt contammg a mum' used The product after the two stage precipitator treat valent cation to the mixture in an amount of 0.026 to 6.6 ment contained less than one iish eye per square inch. gram? of said Sint per gallon of Solutlon; passing said mix' Examination of these examples Shows that products ture into the iniiuence of a direct current electrostatic with a large number of fish eyes can be satisfactorily field n th? range of 8,00 to 33,000 Yolts, Per mh of elefi' treated by om. invention. While a goed product can be trode spacing, recovering polybutadiene in solution in said improved, it is believed that the invention will nd its Solvent as the emuent from Said electrostatic eld 'as a greatest use where the product from the quench step conproduct of the Procfss remfimg the charge from the tains a considerable number of iish eyes where a satisfacelectrodes and ushmg Preclpltated gel from the elec tory product is ditiicult to obtain without the addition nodes' of salt. More speciiically, we believe our invention will 2' In the Poss for Pmdufmg polybutfjdlefe Whereln have its greatest utility wherein the product from the re- .13'butad1ene 1S polymenzed 1.a polymerlzatlqn zonefn actor emuent has over 75 sh eyes per Square inch or inert solvent lfor the polybutadiene and wherein gels inwhere the simple electrical treatment will not provide a Soiuble m said Splvent al-.e produced as `a.bypr0duct. of product having less than 5 ish eyes per square inch. Sa 1d polyfnemzauo'n 'Ehe unprovmeflt Whlch com prlses From Example II, it will be seen that a considerable iin- Wlthqrawmg from sin@ polymerization Zone a rmx/[ure provement is obtained and, in all cases, wherein salt was of Sald Solvfft contamlg polybufadene and 361i adding added, over 90 percent of the sh eyes have been removed a salt containing a multivalent cation to the mixture in an and usually over 97 percent of the sh eyes can be remount O f 0-02 6 t0 6-6 grams 0f Salt Per gallon 0f 80h1- moved by the process of our invention tion, passing said mixture into the in-iluence of a irst di- Although the invention is described as specically direct current electrostatic iield in the range of 1100 to 8800 rected to the removal of gel or cross-linked polymer from volts per inch electrode spacing, passing the effluent from the rst electrostatic treatment into the influence of a second direct current electrostatic eld in the range of 11,000 to 28,0010 kvolts per inch electrode spacing, recovering polybutadiene in solution in said solvent as the erliuent from said second electrostatic field as a product of the process, removing the charge from the electrodes and ushing precipitated gel from the electrodes.

3. In the process for producing polybutadiene wherein 1,3-butadiene is polymerized in la polymerization zone in the presence of a nely divided alkali metal catalyst and an inert solvent for the polybutadiene and wherein gels insoluble in said solvent are produced as a byproduct of said polymerization, the improvement which comprises withdrawing from said polymerization zone a mixture of said solvent containing polybutadiene dissolved therein, gel, and catalyst, adding a `salt containing a multivalent cation to the mixture in an amount of 0.026 to 6.6 grams ofr said salt per gallon of solution, passing said mixture into the inuence of a rst electrostatic field in the range of 1100 to 8800 volts per inch electrode spacing, passing the eiuent from the rst electrostatic treatment into the influence of a second direct current electrostatic eld in the range of 11,000 to 28,000 volts per inch electrode space, recovering polybutadiene dissolved in said solvent as the eiuent from said second electrostatic eld as a product of the process, removing the charge from the electrodes and flushing precipitated gel and catalyst from the electrodes.

4. The process of claim 3 wherein said salt is aluminum sulfate.

5. The process of claim 3 wherein said salt is aluminum chloride.

References Cited in the tile of this patent UNITED STATES PATENTS 1,591,472 De Brey July 6, 1926 1,990,213 Winkler et al. Feb. 5, 1935.l 2,086,666 Fisher luly 13, 1937 2,130,789 Campbell Sept. 30, 1938 2,247,065 yPauli et al. June 24, 1941 2,463,610 Glassmire et al. Mar. 8, 1949 2,485,335 Tyson Oct. 18, 1949 2,825,686 Greene et al. Mar. 4, 1958 

1. IN THE PROCESS FOR PRODUCING POLYBUTADIENE WHEREIN 1,3-BUTADIENE IS POLYMERIZED IN A POLYMERIZATION ZONE IN AN INERT SOLVENT FOR THE POLYBUTADIENE AND WHEREIN GELS INSOLUBLE IN SAID SOLVENT ARE PRODUCED AS A BYPRODUCT OF SAID POLYMERIZATION, THE IMPROVEMENT WHICH COMPRISES WITHDRAWING FROM SAID POLYMERIZATION ZONE A MIXTURE OF SAID SOLVENT AND GEL, ADDING A SALT CONTAINING A MULTIVALENT CATION TO THE MIXTURE IN AN AMOUNT OF 0.026 TO 6.6 GRAMS OF SAID SALT PER GALLON OF SOLUTION, PASSING SAID MIXTURE INTO THE INFLUENCE OF A DIRECT CURRENT ELECTROSTATIC FIELD IN THE RANGE OF 800 TO 33,000 VOLTS PER INCH OF ELECTRODE SPACING, RECOVERING POLYBUTADIENE INSOLUTION IN SAID SOLVENT AS THE EFFLUENT FROM SAID ELECTROSTATIC FIELD AS A PRODUCT OF THE PROCESS, REMOVING THE CHARGE FROM THE ELECTRODES AND FLUSHING PRECIPITATED GEL FROM THE ELECTRODES. 